When a conveyor belt is required to operate in environmentally uncontrolled conditions where it is subjected to abrasives, its life span is considerably shortened by frictional contact between relatively movable parts in the presence of the abrasives. Even in the absence of grit and other abrasives, belt wear in the vicinity of relatively movable parts is the most significant factor in terminating the useful life span of the belt.
In modular conveyor belts, modules are traditionally interdigitated at opposite ends and linked together by means of pivot rods extending through the interlaced belt link ends in a pattern forming a conveyor surface. To pass over sprockets, the modules need to have articulated hinges, for example, conventionally provided by means of the pivot rods.
A major problem encountered is the accumulation of dirt and grit in the vicinity of the pivot pin wear surfaces, causing accelerated abrasive wear and early belt failure.
An excellent conveyor system that is drivable in both directions, easy to clean, and easy to track is disclosed in J. M. Lapeyre's U.S. Pat. No. 4,925,016, entitled "Heavy Duty Modular Conveyor Belt And Sprocket With Unique Tracking," issued May 15, 1990, and assigned to the assignee of this invention. The modular plastic belt disclosed therein is a heavy-duty modular conveyor belt that has a smooth load-carrying surface and uses a single transverse tooth member in each module as the means for driving the belt. The belt comprises a number of individual modules pivotally joined by pivot rods. The modules, preferably formed by injection molding, include link ends on both ends, which intermesh with link ends of other modules. Pivot rods in holes formed by apertures in the intermeshed link ends hold the belt together and permit hinged articulation about a sprocket. The belt is driven by a sprocket that contacts the transverse tooth member of the belt at the center of the pitch line of each module. The single tooth member used is easy to clean because it has few hard-to-reach surfaces. Tracking is provided by separate sprocket teeth received in spaces between intermeshed link ends of adjacent modules. The tracking spaces provided by the disclosed belt are formed between each link end by sizing the thickness of the sprocket-side portion of each link end less than the thickness of the load-side portion. Because the pivot aperture of each link end is in the narrower sprocket-side portion, the pivot rod bearing structure in the link ends is discontinuous about the pivot rod, thereby exposing the pivot rod to dirt and grime as in Lapeyre U.S. Pat. No. 4,925,016. Such pivot rod bearing structure is herein termed "open hinge." Conversely, "closed hinge" refers to structure that encompasses the entire pivot rod so that it is not exposed to dirt and grime. Such contamination between the pivot rod bearing structure and the movable pivot rods can severely shorten the useful lifetime of the belt.
Closed-hinge conveyor belts providing tracking in close proximity to the hinges by means of sprockets having teeth that are received in the belt structure are exemplified in J. M. Lapeyre's U.S. Pat. No. 3,870,141, issued Mar. 11, 1975, and entitled "Modular Belt" and in U.S. Pat. No. 3,724,285, issued Apr. 3, 1973, entitled "Conveyor Drive," and reissued Jul. 22, 1980 under Reissue No. Re. 30,341. None of the prior art references, all of which are assigned to the assignee of this invention, however, shows a belt with tracking spaces provided by a recess in the link ends for receiving the tracking teeth of sprockets.
It has been conventional in the prior art as represented in the aforementioned Lapeyre U.S. Pat. No. 4,952,016, for example, to form notches in the link ends for accommodating mating tracking teeth, resulting in open hinges exposing pivot rods to grime and grit. Thus, belt systems employing tracking teeth operable in notches in the link end structure otherwise normally surrounding the pivot rods have had short lives and are not adaptable for use in abrasive environments.
Accordingly, along with the general objective of providing improved conveyor belt systems with tracking means that resolve the foregoing problems, it is the specific objective of this invention to produce link end hinging structure having tracking tooth notches adapted for use in abrasive environments.